Gear-up and gear-collapse accidents (what I call collectively ‘Landing Gear-Related Mishaps,’ or LGRMs) account for nearly half of all reported incidents in certified, piston-powered retractable gear (RG) airplanes. There is a fairly strong correlation between these LGRMs and, of all things, a weather phenomenon-strong or gusty surface winds. How might surface winds exceeding 15 knots contribute to gear up and gear-collapse accidents?
A ‘gear up’ mishap is one where the pilot fails to lower the landing gear prior to touchdown, with no apparent mechanical cause. It’s the classic pilot-distraction event…something has diverted the pilot’s attention to the point he or she misses this vital step in landing the airplane. That ‘something’ might sometimes be unusual visual cues created by the wind.
Let’s say you normally fly downwind, lowering the landing gear when abeam your touchdown spot and settling into a 500 – 600 foot per minute descent rate as you turn base and then onto final approach. Do this a few hundred times and you have a very good visual idea of what the descent angle and your progress across the ground will look like.
Now come into the same pattern (or a strange one) with a strong wind favoring the active runway. Your downwind leg will be very rushed as the wind increases groundspeed. If you are not procedurally perfect you may miss extending gear at the ‘usual’ time and find yourself high and wide when turning base. Now you feel you’re going too fast, so you reduce power, crabbing into the wind and turning final in your zeal to make it ‘back’ to the airport. At this point, long and high on final approach with the gear still up, you’re now plodding into a strong headwind. Your apparent progress across the ground slows, and your angle of descent looks steeper than normal because you’re being held back by the wind. Progress makes it look as though your gear is down. You might even find yourself adding power because it feels like you’re not covering ground quickly and it looks as though your descent angle will bring you in short of the runway. At this stage lowering the landing gear-associated with slowing down and increasing descent rate-gets further from your mind. The added power moves your throttle far enough away from idle that the gear warning horn doesn’t sound, and if you’re not lucky your first indication that the gear is still up will be the awful sound of the propeller making its first gouge into the pavement.
The problem is more acute if you’re coming in on a base leg or if directed to land from a straight-in approach. Here’s you’re already behind the experience curve because there’s no set point where you’re used to lowering the landing gear. If you get caught up in the low groundspeed/high angle of descent visual cues of landing into a strong headwind, events are working against you to catch the gear before you touch down. A gear up can’t happen to you? That’s what about three more U.S. pilots say every week.
Add bouncing from low-level turbulence and you can easily see the distraction scenario build. Are visual cues the cause? Although it’s possible to land gear up out of an instrument approach, the record shows that gear-up landings are almost always a VFR event. Instrument pilots have more direct indications of progress toward the runway and generally a more ingrained sense of exactly when to lower the gear (usually at the final approach fix).
Insider’s tip: Avoid wind-related gear-up landings by always extending your landing gear at the same place whether on a visual or an instrument approach. Make it a firm habit to re-check gear position as soon as you complete your turn onto final approach or, if coming straight in, when passing through the traffic pattern altitude.
A ‘gear collapse’ mishap is when the gear is put down for landing but does not remain down, again with no identified mechanical reason (although, to be honest, many gear rigging and fatigue issues are not discovered until after the mishap report is complete). How can wind contribute to this type of LGRM?
Strong and especially gusty surface winds and crosswinds make directional control on landing more difficult. It was standard practice in some very light, early airplanes with flaps (the 1940s Cessna 140, for instance) to retract flaps immediately after touchdown to ‘put more weight on the wheels’ for braking and directional control, and to ‘spoil lift’ to keep the gusts from inducing bounces during the rollout. This thinking, and a natural rush many pilots feel to ‘clean up’ the airplane after landing, leads to an instructional/post-instructional mindset to retract the flaps during the landing roll. That’s fine, as long as the pilot gets the right handle in hand. The record shows, unfortunately, that many times in the rush to retract flaps the pilot inadvertently moves the landing gear handle instead. This unlocks the landing gear and very often results in a gear collapse (about four times a week in the U.S., on average). Strong and gusty winds, contributors to control difficulty on landing and distractions in their own right, might make pilots more inclined to use the ‘flap retraction during the landing roll’ technique and to reach for the wrong control in their haste.
Should the safety systems prevent gear collapse? Most RG airplanes have a ‘squat switch’ on at least one landing gear leg, designed to block power to the landing gear motor when there’s weight on the wheels. It takes very little movement of a gear leg, however, to flex the squat switch into a ‘flight’ position-so a gust picking up a wing slightly, or bouncing over an expansion joint on the runway, may be just enough to override the safety switch. If this coincides with a movement of the gear handle in the cockpit, then the motor starts to run, the gear unlocks, and when weight comes back down on the gear leg the landing gear collapses.
Insider’s tip: Even in the strongest winds, do not reconfigure the airplane after landing until you’ve cleared the runway and preferably come to a complete stop that gives you time to properly identify the flap control.
BOTTOM LINE: Nearly half of all reported RG mishaps are either gear up or gear collapse incidents. Strong and gusty surface winds can create distractions, visual cues and perceived operational needs that contribute to many LGRMs. Practice landing gear discipline to avoid joining more than one more pilot every day that suffers a landing gear-related mishap.
For more on LGRMs see www.thomaspturner.com.